horse has 8 distinct synonyms spread across 5 of its 6 senses. Each sense below keeps its own list, because a synonym belongs to a meaning and not to a word: swapping one sense's substitute into another sense's sentence is how a thesaurus makes writing worse. WordNet records no antonym for it — antonymy is a relation between word forms rather than concepts, so it is deliberately sparse.
Counts are distinct word forms across every sense. A synonym that appears under three senses is counted once here and shown three times below, under each sense it belongs to.
solid-hoofed herbivorous quadruped domesticated since prehistoric times
a padded gymnastic apparatus on legs
troops trained to fight on horseback
“500 horse led the attack”
Synonyms, antonyms and the broader and narrower relations for horse come from Princeton University’s WordNet. Full sources and licences.